Microsporidia are emerging human and veterinary pathogens that cause a wide range of disease syndromes. The unique structure of the microsporidia is the polar tube, which is used to infect the host cell. The investigators have characterized the polar tube proteins (PTP's) and have identified putative polar tube associated proteins (PTAP's) of several microsporidian species and propose to further characterize and localize these proteins in additional species of microsporidia. The specific aims are to, 1) identify and analyze conserved structural motifs of PTP's to characterize their function, 2) identify and characterize PTAP's that may function in polar tube formation and function, 3) localize the PTP's and PTAP's during development (3a) and eversion (3b) of the polar tube, and 4) characterize the mechanism of polar tube assembly using recombinant proteins in vitro. It is anticipated that the results of these studies will further studies to identify drug targets for interfering with polar tube development and/or function in future studies.